System and method for machining blades, blisks and aerofoils

ABSTRACT

Systems and method relating to machining parts include a CNC system including CNC machining tools, and a computer including a processor and a computer-readable medium, wherein the computer-readable medium encodes instructions of a single NC program that, when run on the processor, causes the computer to control a selected CNC machining tool to perform operations including alternating between (i) moving the selected CNC machining tool along a semi-finishing toolpath segment using a first set of spindle speed and feed rate values to remove a next portion of rough stock material in a next region of a part being manufactured, and (ii) moving the selected CNC machining tool along a finishing toolpath segment to remove a semi-finishing thickness portion of the part in the next region, wherein the first set of spindle speed and feed rate values are different from the second set of spindle speed and feed rate values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims priority to,U.S. application Ser. No. 15/146,617, filed on May 4, 2016, andpublished on Apr. 6, 2017, as U.S. Patent Publication No.US-2017-0095865-A1, which claims priority to U.S. ProvisionalApplication No. 62/235,903, filed on Oct. 1, 2015. The disclosures ofthe prior applications are considered part of and are incorporated byreference in the disclosure of this application.

BACKGROUND

This specification relates to machining blades, bladed disks, blisks andaerofoils, such as integrally bladed rotors or stators for turbineengines.

Blades are traditionally machined in large sections, one side at a timeor in multiple levels, all of which have the sole purpose of providingsupporting material to reduce vibration during the machining process.The machining process for a blade typically involves three separateprocess steps: (1) roughing out the blade, (2) performing asemi-finishing process on the blade, and (3) performing a finalfinishing process to get the final desired blade shape. Themanufacturing costs of such traditional machining processes can berelatively high due to the time needed to perform the separate processsteps of the machining process and the tool wear caused thereby.

In addition, when the final blade is thin (as is common for aerofoils)the material being machined gets sequentially thinner in each separateprocessing step. This means that the part being manufactured becomesless strong and more subject to distortion during the machining process.This can lead to inaccuracies and poor surface finish in the finalproduct. In order to address this issue, some have employed a roughingout process that creates a terraced support structure to provideadditional strength to the part for the subsequent semi-finishing andfinishing processes.

FIGS. 2A-2B show an example of a terraced support structure created by atraditional Computer Numerical Control (CNC) milling process. After theinitial process step of roughing out a blade 200, the blade 200 includesboth the stock material 210, 212 left after the roughing operation, andalso the finished desired blade form 220, which is still to be revealedin the CNC milling process. As shown in FIG. 2A, the material left on acomponent being created forms a support structure that is terraced inshape.

This terraced shape has two disadvantages: first, the non-uniform shapeof the stock material 210, 212 has inherent weaknesses, and second, thenon-uniform shape of the material means the milling cutter encountersuneven amounts of stock material that can lead to tool damage, wear andpush off, leaving excess material on the component. FIG. 2B shows alarger view of a portion 230 that includes rough stock material of theblade 200 from FIG. 2A. As shown, extra stock material 240 isencountered by a cutting tool 250 when traditional terraced stockmethods are used in a CNC process.

SUMMARY

This specification describes systems and methods relating to machiningblades, bladed disks, blisks and aerofoils, such as integrally bladedrotors or stators for turbine engines, which can be used in aerospaceand power generation applications. In particular, the traditionallyseparate process steps of semi-finishing and finishing can be combinedas described herein. By combining semi-finishing and finishing, amachining tool can be directed to do a few semi-finishing slices, andthen jump back up and do a couple finishing slices, and then jump backdown and do a few more semi-finishing slices, etc. Because the machiningtool is not going all the way down with the semi-finishing, the strengthin the component can be retained. Thus, as the machining tool works itsway down, a self-supporting thickness of material is maintained. Thiscan allow one to increase the size of the component sections/levelsprocessed and reduce the number of component sections/levels that needto be processed. In some cases, an entire blade can be machined(semi-finished and also finished) from top to bottom in one go.

In general, one or more aspects of the subject matter described in thisspecification can be embodied in a method including: first directing,using a single Numerical Control (NC) program, a single machining toolin a CNC system along a semi-finishing toolpath to remove a portion ofrough stock material over a first distance, leaving behind asemi-finishing thickness portion; second directing, using the single NCprogram, the single machining tool in the CNC system along a finishingtoolpath to remove the semi-finishing thickness portion over a seconddistance, wherein the second distance overlaps the first distance, andthe second distance is shorter than the first distance by an offsetdistance set for the part; and repeating the first directing and thesecond directing, using the single NC program, such that the partremains self-supporting as the single machining tool alternates betweensemi-finishing and finishing toolpaths to form the part.

Aspects of this embodiment may include one or more of the followingfeatures. The part can be a blade or other components. The rough stockmaterial can be a non-terraced rough stock, e.g., for the blade. Each ofthe first directing and the second directing can track fully around thepart, and the repeating can continue for a full length of the part,until completion. Further, the first and second directing can be kept toa minimum between each repetition thereof for a given part, and thefirst directing (semi-finishing) can be limited to extend only a shortdistance farther than the second directing (finishing); for example, thefirst directing can consist of performing two to five semi-finishingslices, and the second directing can consist of performing two to fourfinishing slices.

The single NC program can contain multiple sets of spindle speed andfeed rate controls that change depending on a current segment beingeither a semi-finishing segment or a finishing segment. The part can bean aerofoil, and the single NC program can use the multiple sets ofspindle speed and feed rate controls to slow the single machining toolfeed rate and spindle speed around leading and trailing edges of theaerofoil. The multiple sets of spindle speed and feed rate controls caninclude a first spindle speed and feed rate for concave and convex facesof the part, and a second spindle speed and feed rate for leading andtrailing edges of the part.

The single NC program can specify a first set of spindle speed and feedrate values for the semi-finishing toolpath and a second set of spindlespeed and feed rate values for the finishing toolpath, wherein the firstset of spindle speed and feed rate values are different from the secondset of spindle speed and feed rate values. The semi-finishing toolpathcan include semi-finishing segments, the finishing toolpath can includefinishing segments, the first set of spindle speed and feed rate valuescan include different spindle speed and feed rate values for differentones of the semi-finishing segments, and the second set of spindle speedand feed rate values can include different spindle speed and feed ratevalues for different ones of the finishing segments.

The method can include gradually speeding up and slowing down spindlespeed and feed rate of the machining tool, by the same NC program,across a set distance when approaching or leaving one or more predefinedportions of the part. The one or more predefined portions of the partcan include corners of the part. The predefined portions of the part caninclude leading and trailing edges of the part.

In addition, one or more aspects of the subject matter described in thisspecification can be embodied in a non-transitory computer-readablemedium encoding a Numerical Control (NC) program that, when run, causesa Computer Numerical Control (CNC) system to perform operations inaccordance with any of the method embodiments. Furthermore, one or moreaspects of the subject matter described in this specification can beembodied in a non-transitory computer-readable medium encoding a program(e.g., a Computer Aided Manufacturing (CAM) program) that generates suchNC programs in accordance with any of the NC program and/or methodembodiments.

One or more aspects of the subject matter described in thisspecification can also be embodied in a system including two or more CNCmachining tools and a computer including a processor and acomputer-readable medium, wherein the computer-readable medium encodesinstructions of a single NC program that, when run on the processorcauses the computer to control a selected one of the two or more CNCmachining tools to perform operations including alternating between (i)moving the selected one of the two or more CNC machining tools along asemi-finishing toolpath segment using a first set of spindle speed andfeed rate values to remove a next portion of rough stock material in anext region of a part being manufactured, and (ii) moving the selectedone of the two or more CNC machining tools along a finishing toolpathsegment to remove a semi-finishing thickness portion of the part in thenext region, wherein the first set of spindle speed and feed rate valuesare different from the second set of spindle speed and feed rate values.

Aspects of this embodiment may include one or more of the followingfeatures. Each respective set of spindle speed and feed rate values canspecify spindle speed and feed rate values for each point connectingsegments of a toolpath. The operations can include slowing feed rate andspindle speed of the selected one of the two or more CNC machining toolsaround leading and trailing edges of the part. Further, the operationscan include gradually speeding up and slowing down spindle speed andfeed rate of the selected one of the two or more CNC machining toolsacross a set distance when approaching or leaving one or more predefinedportions of the part. Finally, the CNC system can include a mediumencoded program in accordance with any of the CAM program, NC program,and/or method embodiments.

Particular embodiments of the subject matter described in thisspecification can be implemented to realize one or more of the followingadvantages. Blades, bladed disks, blisks, aerofoils, etc., can bemachined in less time and with superior finish. While more than one toolcan be used in a Computer Numerical Control (CNC) system, a single CNCtool (selected from multiple available CNC tools in the CNC system) canbe used at a time in a combined semi-finishing and finishing process,and tool life can be maintained or even extended using variable spindlespeed and feed rate controls with the single CNC tool used in thecombined semi-finishing and finishing process. The combinedsemi-finishing and finishing process can reduce stress exerted on a partduring the part's manufacture, which can improve the quality of thefinished part, and thus reduce the part's defect rate and probability offailure.

Required surface finish can be achieved with reduced cycle times, andblending between different sections/levels of a machined part can beimproved. Mismatch between individually machined sections/levels anddistortion away from the desired final blade form can be reduced.Moreover, surface finish quality can be improved across the entirelength of a blade by changing the spindle speed and feed rate used witha CNC tool multiple times, in a controlled fashion, through a runningcycle. In some implementations, variable spindle speed and feed ratecontrols can be used to ensure that semi-finishing and finishingsegments of a single toolpath are running at optimal parameters so as toensure a good tool life in addition to the improvements in resulting themachined part.

The details of one or more embodiments of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of theinvention will become apparent from the description, the drawings, andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a Computer Numerical Control (CNC) system.

FIGS. 2A-2B show an example of a terraced support structure created by atraditional CNC milling process.

FIG. 3 shows an example of a support structure, in accordance with thesystems and techniques of this disclosure, which can be created by a CNCmilling process as a blade is machined.

FIGS. 4A-4H show a detailed example of a blisk machined using thesystems and techniques described herein.

FIGS. 5A-5E show a software simulation of a combined semi-finishing andfinishing process in accordance with the detailed example of FIGS.4A-4H.

FIGS. 6A-6F compare various machining processes with reference to ageneralized aerofoil.

FIGS. 7A-7B show top views of examples of toolpaths with respect to thegeneralized aerofoil of FIG. 6A.

FIG. 8 is a flow diagram of an example method for machining a part usinga CNC system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows an example of a Computer Numerical Control (CNC) system100. A computer 110 includes a processor 112 and a computer-readablemedium, such as a memory 114, a storage device, or both, to storeinstructions of one or more computer programs 116 that run on theprocessor 112. The computer 110 can be connected to a network 140, whichcan be a private network, a public network, a virtual private network,etc. The processor 112 can be one or more hardware processors, which caneach include multiple processor cores. The memory 114 can include bothvolatile and non-volatile memory, such as Random Access Memory (RAM) andFlash RAM. The computer 110 can include various types of computerstorage media and devices, which can include the memory 114.

A computer program 116 can present a user interface (UI) 122 on adisplay device 120 of the computer 110, which can be operated using oneor more input devices 118 of the computer 110 (e.g., keyboard andmouse). Note that, while shown as separate devices in FIG. 1, thedisplay device 120 and/or input devices 118 can also be integrated witheach other and/or with the computer 110, such as in a tablet computer.In addition, the CNC system 100 includes a machining apparatus 170,which includes one or more computer controlled machine tools. These caninclude, but are not limited to, all types of milling cutter tools,including those with ball nose, tapered, tip radius and barrelgeometries. In addition, the machining apparatus 170 can include othercomponents and systems, such as rotatable platforms/attachments (e.g.,for five-axis milling processes) and cleaning systems (e.g., sprayedwater cleaning systems).

The machining apparatus 170 can include its own computer 110, withprocessor 112, memory 114, computer program 116, etc. For example, insome implementations, the computer 110 and the machining apparatus 170can be integrated together, without a network 140 connecting them. Asanother example, the machining apparatus 170 can include a computer thatruns a Computer Aided Manufacturing (CAM) program which receives, asinput, a model generated by a Computer Aided Design (CAD) program 116and/or a Computer Aided Engineering (CAE) program 116 on a separatecomputer 110.

Alternatively, the machining apparatus 170 can simply be the machinetools and other manufacturing components that are controlled by thecomputer 110, and the computer program 116 can be a CAM program, whichcan receive as input a model generated by CAD and/or CAE programslocated elsewhere. For example, one or more remote computer systems 150,which are accessible by the computer 110 via the network 140, caninclude CAD programs and CAE programs used to generate models that areinput to and processed by a CAM program 116.

In any case, a CAM system can be provided that allows a user 190 tointeract with a model 132 and readily generate a numerical control (NC)program 130 to operate machining apparatus 170. In the example shown,the model 132 is a 3D model of a particular blisk, but many differenttypes of models can be used with the system and techniques describedherein. Further, in some implementations, the NC program 130 runs on theprocessor 112 to control the machining apparatus 170 directly connectedthereto. In some implementations, the NC program 130 is output(potentially after conversion to a new program format 160) to themachining apparatus 170 to run on its local processor.

When generating the NC program 130, the CAM system can be used to assignspindle speed and/or feed rate parameters at each point from hundreds ofpoints that make up a toolpath. Using these assigned parameters, the CAMsystem can generate NC programs 130, 160 that can gradually speed up andslow down spindle speed and feed rate of the machining tool across a setdistance when approaching or leaving one or more predefined portions ofthe part. For example, speed up and slow down rates can be different forconcave and convex faces of a part and/or for leading and trailing edgesof the part. Note that determination of the values for the spindlespeeds and feed rates can be determined based on material to be used forthe part to be manufactured, the tool to be used, and any guidelinesprovided by the tool manufacturer for acceptable operational parametersfor the tool. Testing can also be used determine appropriate speeds tobe used with the tool for a given part to be manufactured. Note thatcomponents can have certain resonances based on how thick or thin theyare, and the tools used in a CNC machine can generate differentvibrational frequencies based on the speeds at which they are run whenmanufacturing a given part. Thus, testing can be used to avoidinappropriate harmonics being generated between the tool and thecomponent.

FIG. 3 shows an example of a support structure, in accordance with thesystems and techniques of this disclosure, which can be created by a CNCmilling process as a blade is machined. As shown, support structure 300,302 is constructed and used for the manufacture of a blade in a processthat combines semi-finishing and finishing machining steps. A firstsmall portion of the support structure 300, 302 is removed by a millingcutter 340 to reveal a semi-finishing thickness portion 310, 312 of thecomponent being manufactured. Then, a first small portion of thesemi-finishing thickness portion 310, 312 of the component is removed bythe milling cutter 340 to reveal the finished blade 320. Thesealternating steps can be repeated down the entire length of the blade,such that the blade is self-supporting for the entire time the componentis being semi-finished and finished, without the use of a terracedstructure.

In this example, the portions removed in each of the alternatingsemi-finishing and finishing process steps are small, but this need notbe the case in all implementations. In general, the step over/step downvalue used between the alternating semi-finishing and finishing canchange based on the specific component (e.g., a specific aerofoil) beingmanufactured, surface finish requirements, and/or any cutting conditionlimitations. Note that the number of slices within any given toolpathcan vary from being in the 10's, 100's, 1000's and beyond. However,using the systems and technique described herein, the semi-finishingslices proceed ahead of the finishing slices by as small an amount aspossible, in light of the specific machining context, so as to providethe supporting structure and retained strength while machining thespecific part (e.g., the specific aerofoil).

An offset distance 330 between semi-finishing and finishing toolpathsegments allows the milling cutter 340 to perform the semi-finishing andfinishing operations in close proximity to each other. An NC (NumericalControl) program that controls the milling cutter 340 contains bothsemi-finishing and finishing segments, and these segments alternate asthey progress down the blade. This NC program includes an offset valuefor the offset distance 330 that allows a number of semi-finishingsegments to be machined before alternating to a finishing segment andthen back and forth between semi-finishing and finishing segments. Inaddition, the NC program can also contain multiple sets of spindle speedand feed rate controls that change and alternate depending on thesegment either being semi-finishing or finishing type.

Use of this pre-machined support structure means that the blade isself-supporting as the machining process progresses down the blade. Notethat the use of non-terraced stock (compare FIG. 3 with FIG. 2B)provides a consistent cutting condition for the cutting tool, which canimprove tool life and component quality while also reducing machiningtime. The component can be semi-finished and finished using a singleNumerical Control (NC) program that tracks fully around the blade andprogresses until completion. In addition, this process can also beapplied when machining the component in separate sections/levels and notall in one go.

In some implementations, the whole component can be finished at once,and not a side at a time, which can reduce distortion and increasequality. In some implementations, a whole blade can be finished at onceand not in a level by level method, thus potentially eliminatingpossible distortion and miss-match between levels and increasingquality. In addition, the NC program can contain multiple sets ofspindle speeds and feed rates for different segments of thesemi-finishing and for the finishing, which enables fine-tuning to takeplace for the amount of material being removed, which can optimizesurface finish, quality and cycle time for the component.

FIG. 4A shows an aero engine blisk 400 machined to a condition readystate for the systems and techniques described herein to begin. FIG. 4Ashows a blisk, which is a disc 402 with roughed blades 404 (e.g.,roughed aerofoils) made from rough stock material that is ready forfinishing. FIG. 4B shows a close up of two roughed blades 404 with thesame stock material as from FIG. 4A.

FIG. 4C shows a first level rough, where an initial section 406 of eachblade 404 has been roughed to its near net shape, plus the stockmaterial, e.g., stock material +0.6 mm. The blades 404 are now ready forthe combined semi-finishing and finishing process.

FIG. 4D shows a close up of a first level finish 408 of a blade 404,e.g., finished to +0.0 stock material. The first level of the blade 404has been machined using the combined semi-finishing and finishingprocess, e.g., stock material +0.0 mm. The process provides aself-supporting structure, where each sub-level of this first level issemi-finished and then finished, and this alternating process progressesdown to the bottom of this first level. Note that a traditional methodwould semi-finish all of the sub-levels of this level, progressing tothe bottom of the first level and then repeat with the finishing. Thismeans that after the traditional semi-finishing, +0.2 mm stock materialwould leave the blade 404 thinner, weaker and less stable for thefinishing passes.

FIG. 4E shows a second level rough finish 410 of blade 404, roughed tonear net shape+stock material. The first level of the blade 404 on theblisk 400 is now finished, and the second level of the blade 404 isroughed to near net shape: stock material +0.6 mm. The blade 404 is nowready for the combined semi-finishing and finishing process again.

FIG. 4F shows a close up of the second level finish 412 of the blade404, e.g., finished to +0.0 stock material. The second level of theblade 404 has been machined using the combined semi-finishing andfinishing process, e.g., finished to stock material +0.0 mm. Again, theprocess provides a self-supporting structure, where each sub-level ofthis second level is semi-finished and then finished, and thisalternating process progresses down to the bottom of this second level.As mentioned before, note that a traditional method would semi-finishall of the sub-levels of this level, progressing to the bottom of thesecond level and then continuing with the finishing. This means that,after the traditional semi-finishing, the +0.2 mm stock material wouldleave the blade 404 thinner, weaker and less stable for the finishingpasses.

FIG. 4G shows a third level rough finish 414 of the blade 404, roughedto near net shape+stock material. The first and second levels of theblade 404 on the blisk 400 are now finished 408, 412, and the thirdlevel of the blade 404 is roughed to near net shape, e.g., to stockmaterial +0.6 mm. The blade 404 is now ready for the combinedsemi-finishing and finishing process again.

FIG. 4H shows a close up of the third level finish 416 of the blade 404,e.g., finished to +0.0 stock material. The third level of the blade 404has been machined using the combined semi-finishing and finishingprocess, e.g., stock material +0.0 mm. Again, the process provides aself-supporting structure, where each sub-level of this third level issemi-finished and then finished, and this alternating process progressesdown to the bottom of this third level. As mentioned before, note that atraditional method would semi-finish all of the sub-levels of thislevel, progressing to the bottom of the second level, and then repeatwith the finishing. This means that, after the traditionalsemi-finishing, the +0.2 mm stock material would leave the blade 404thinner, weaker and less stable for the finishing passes.

FIGS. 5A-5E collectively show a software simulation 500 of a combinedsemi-finishing and finishing process for a blade 502, in accordance withthe detailed example of FIGS. 4A-4H. For example, FIGS. 5A-5E show theblade 502 in a close-up view of a blisk 504 being finished by a cuttingtool 505. FIG. 5A shows an initial (in progress) semi-finishing 506(e.g., roughed to +0.4 mm stock) in the combined semi-finishing andfinishing process at a first level 508 (e.g., roughed to +0.6 mm stock).The blade 502 is visibly thinner at the top 510.

FIG. 5B shows an in-progress finishing 512 of the same initial portionof the blade 502 (e.g., after the cutting tool 505 has jumped back up tothe top 510 of the blade 502 from the semi-finishing) in the combinedsemi-finishing and finishing process at the first level. As such, thecutting tool 505 has started to finish the blade 502 to +0.0 mm stock.Several semi-finishing passes have progressed down the blade 502, e.g.,to +0.4 mm stock in a region 514, and a first level of the blade 502 hasbeen roughed to +0.6 mm stock in a region 516. Again, the blade 502 isvisibly thinner in the finished section at the top 510 due to thefinishing. During this process, the blade 502 is more fully supportedduring finishing because of strength retained by having semi-finishedstock (in the region 514) and rough stock (in the region 516) to supportthe blade 502 as the finishing 512 progresses down the blade 502.

FIG. 5C shows a resulting first level 518 of the blade 502 after thefirst level is done, at which time most of the blade's first level isfully finished, and small portions of the blade's first level remain atthe semi-finished and roughed stock dimensions. In a region 520, forexample, the first level of the blade 502 is now finished to +0.0 mmstock. Semi-finishing passes have progressed down the first level of theblade 502 to +0.4 mm stock in a region 522. The first level of the blade502 has been roughed to +0.6 mm stock in a region 524. The second levelof the blade 502 can now be roughed.

FIG. 5D shows an initial in-progress semi-finishing 526 in the combinedsemi-finishing and finishing process, now at the second level, after thesecond level has been roughed to +0.6 mm stock down to a region 532. Inan upper region, the first level of the blade 502 is now finished to+0.0 mm stock, and the combined semi-finishing and finishing processresumes, e.g., in a region 530, with a semi-finishing pass 526 to +0.4mm stock proceeding down to a position 534.

FIG. 5E shows an in-progress finishing 528 performed after the firstsemi-finishing pass 526. After this first semi-finishing pass, thecutting tool 505 jumps back up to a higher position on the blade 502 tomachine a finishing pass 528. Note that bottom positions 534 and 536 ofthe cutting tool 505, in FIGS. 5D and 5E, respectively, are differentwith reference to the rough +0.6 mm stock, when performing asemi-finishing pass versus a finishing pass. This difference correspondsto the offset distance 330 discussed above.

In addition, the semi-finishing and finishing toolpaths can havedifferent spindle speeds and feed rates. In some implementations, morethan one set of spindle speeds and feed rates can be included for thesemi-finishing and finishing toolpaths. This can help, for example, whenmachining around the leading and/or trailing edges of an aerofoil, whereit may be desirable to slow the machine feed rate and spindle speedaccordingly. In some implementations, any given toolpath can have twosets of spindle speeds and feed rates, e.g., one for the concave andconvex faces, and another for the leading and trailing edges. Inaddition, in some implementations, the spindle speeds and feed rates canbe gradually sped up and/or slowed down across a set distance whenapproaching or leaving the leading or trailing edge (e.g., corners).This can reduce or eliminate undesirable marks on the component surfacethat may be caused by sudden accelerations/decelerations. In someimplementations, spindle speeds and feed rates can vary for otherreasons, e.g., based on the type, strength and/or thickness of thematerial being tooled.

FIGS. 6A-6F compare various machining processes 601 a-601 d withreference to a generalized aerofoil 600. FIG. 6A shows a cross-sectionof the generalized aerofoil 600 with a roughed thickness 602, asemi-finished thickness 604, and a finished thickness 606. FIG. 6B showsa perspective view of the generalized aerofoil 600 with its roughed,semi-finished, and finished thicknesses. Note that, as the aerofoil 600gets thinner and thinner, the aerofoil 600 can become more unstable andharder to machine. This can have adverse effects on the surface finish,accuracy, geometry shape, and tool life.

FIG. 6C shows a traditional single pass process 601 a, in which the CNCsystem can attempt to machine the aerofoil 600 from a top 608 to abottom 610 in a single pass for each of three distinct processes: (1)roughing 612 from top to bottom, (2) semi-finishing 614 from top tobottom, and (3) finishing 616 from top to bottom. Use of this approach,for example, can cause the aerofoil 600 to get thinner and thinner overthe whole surface area of the aerofoil 600, leaving it weak andunsupported.

FIG. 6D shows a traditional multiple pass process 601 b, in which theCNC system machines the aerofoil 600 in separate levels. This can alloweach level to be handled in three distinct processes: (1) roughing 618 anext level, (2) semi-finishing 620 this next level, and (3) finishing622 this next level. When using this approach, the aerofoil 600 is nolonger getting thinner and thinner over the whole surface area of theaerofoil 600, but this is still occurring within each level. Thus, theprocesses' leaving of the aerofoil 600 weak and unsupported is reducedto a smaller localized area. This is helpful, but the process ofsplitting the aerofoil 600 up into so many levels can lead to otherproblems. For example, the use of multiple levels can result in creatingmultiple blend regions that may require the cutting tool to blend backinto the previous level perfectly without mismatch. Also, each time therough and semi-finished stock is removed, localized distortion of theaerofoil 600 can occur, which means the chance of blending to theprevious level perfectly may be reduced, and the end shape of theaerofoil 600 may not be correct.

FIG. 6E shows a single pass process 601 c in accordance with the systemsand techniques described in this disclosure. The semi-finishing andfinishing of the aerofoil 600 can be performed together. This can allowthe aerofoil 600 to be machined in a single pass/level with only twodistinct processes: (1) roughing 624 from top 608 to bottom 610 and (2)semi-finishing and finishing 626 from top 608 to bottom 610. Use of thissingle pass/level can lead to zero blend regions and zero mismatchbetween blends. Thus, there may be less post-machining processing, suchas polishing. Moreover, this approach can result in improved cuttingtool life and less chance of geometry distortions. Thus, the finishedaerofoil 600 can be more accurate.

FIG. 6F shows a multiple pass process 601 d in accordance with thesystems and techniques described in this disclosure, where the CNCsystem machines the aerofoil 600 in separate levels, but thesemi-finishing and finishing of the aerofoil 600 at each level areperformed together. Thus, the aerofoil 600 is machined in levels, buteach level includes only two distinct processes: (1) roughing 628 a nextlevel and (2) semi-finishing and finishing 630 this next level. The useof this approach can result in fewer levels being needed. Also, therecan be fewer blend regions and less mismatch between blends, the cuttingtool life can be improved, and there can be less chance of geometrydistortion. Likewise, the finished aerofoil 600 can be more accurate,and there can be less need for post-machining processing, such aspolishing. Moreover, in both the approaches of FIG. 6E and FIG. 6F,combining of the semi-finishing and finishing means that the strength ofthe aerofoil 600 can be maintained, since the thickness of thesemi-finished stock is retained as the CNC tool progresses down theaerofoil 600.

In addition, when combining the semi-finishing and finishing describedabove, a large number of parameters can be applied to the toolpath thata machine tool can react to such as, but not limited to, spindle speedand feed rate. This can be important because, when a semi-finishing cutis taking place, the cutting conditions are significantly different fromthose of finishing. This can include factors such as the amount of stockbeing removed, the stepover/stepdown of the cutting tool, and theresonance frequency of the aerofoil 600 at any given point. Thus, it maybe less than ideal to run a semi-finishing pass using the same spindlespeed and feed rate parameters as used in a finishing pass.

FIGS. 7A-7B show top views of examples of toolpaths 700 with respect tothe generalized aerofoil 600 of FIG. 6A. For example, the toolpaths 700include a semi-finishing toolpath segment 702 and a finishing toolpathsegment 704. Machine tool toolpaths can consist of many individualsegments, and in turn those segments can be made up of many small linearsegments, each with a start and end point 705. Traditional toolpaths aregiven a single spindle speed and feed rate for the entire toolpath andall of the segments that it contains. In contrast, FIG. 7A showstoolpaths with spindle speed and feed rate control with differentcombinations 706 and 708 for spindle speed (X and A) and feed rate (Yand B) for the semi-finishing (SF) toolpath segment 702 and thefinishing (FN) toolpath segment 704, respectively, but they arenonetheless constant for the entire segment. For example, the spindlespeed and feed rates can be 100% for each of the combinations 706 and708. In some implementations, even finer control or other types ofcontrol can be provided.

FIG. 7B shows toolpaths 710 with spindle speed and feed rate controlwith different combinations 712 and 714 for spindle speed and feed ratefor semi-finishing and finishing, respectively. Further, the spindlespeed and feed rate can also constantly vary as the cutting tool travelsaround the toolpath segment. For example, there can be a 75% reduction716 of spindle speed and feed rate across a given distance or over anumber of toolpath points 718.

In some implementations, the semi-finishing and finishing passes can beisolated and assigned unique spindle speed and feed rate values that aretuned to the cutting conditions required for the aerofoil or evenspecifically for the pass\level being machined at that time. Further, inaddition to the ability to instantly change spindle speed and feed rate,it may be desirable to gradually change the spindle speed and feed rateover the course of the toolpath segment. This is useful because aninstant change may be hard for a machine tool to perform (a spindlerequires time to speed up or slow down), and suddenly changing either ofthese two parameters while in cut can potentially mark or damage thesurface of the aerofoil.

Thus, gradually changing the spindle speed and feed rate over a givendistance from point A to point B can give the machine tool time to reactand eliminate and surface marking on the aerofoil. This can be veryuseful when machining at very high feed rates and trying to machinearound sharp corners. Machine tools cannot always maintain the high feedrate around the sharp corner. In the traditional case, the spindle willnot know to reduce its speed to compensate for the machine tool movingat a reduced feed rate around the corner, and this can lead tovibration, surface marking and cutting tool damage.

Thus, in some implementations, the CAM system can assign a large numberof different commands to every toolpath point, including assigning adifferent spindle speed and feed rate to each toolpath point. This canfacilitate fine control over of the CNC tool as it moves along thetoolpath, including the ability to gradually speed up and slow down thespindle speed and feed rate as desired based on the part beingmanufactured. This can provide one or more of the following benefits:fine-tuning of semi-finishing segments, fine-tuning of finishingsegments, increased machine tool performance, improved surface finish,reduced surface marking, and improved cutting tool life.

FIG. 8 is a flow diagram of an example method 800 for machining a partusing a CNC system. For example, the method 800 can be used formachining the blade 404 described with reference to FIGS. 4A-4H, theblade 502 described with reference to FIGS. 5A-5E, and the aerofoil 600described with reference to FIGS. 6A-6F. The method 800 can be used, forexample, in the manufacture of blades, blisks, aerofoils, and otherparts.

Using a single NC program, a single machining tool is first directed inthe CNC system along a semi-finishing toolpath to remove a portion ofrough stock material over a first distance, leaving behind asemi-finishing thickness portion (802). For example, referring to FIG.5A, through use of the cutting tool 505 in several semi-finishingpasses, the blade 502 has been tooled to +0.4 mm stock from a roughed+0.6 stock.

Using the single NC program, the single machining tool is seconddirected in the CNC system along a finishing toolpath to remove thesemi-finishing thickness portion over a second distance, wherein thesecond distance overlaps the first distance, and the second distance isshorter than the first distance by an offset distance set for the part(804). For example, referring to FIG. 5B, through use of the cuttingtool 505 in several finishing passes, the blade 502 has been tooled to+0.0 mm stock from +0.4 stock. This occurs, for example, while only partof the blade has undergone semi-finishing passes. The offset distance,for example, can be the offset distance 330, which corresponds to adifference in the bottom positions 534 and 536 shown in FIGS. 5D and 5E.

The first directing and the second directing are repeated, using thesingle NC program, such that the part remains self-supporting as thesingle machining tool alternates between semi-finishing and finishingtoolpaths to form the part (806). For example, referring to FIGS. 5C-5E,sequences of several semi-finishing passes followed by several finishingpasses are repeated. During this time, the blade 502 is tooled to +0.4mm stock from +0.6 mm stock in the semi-finishing passes, and the blade502 is tooled to +0.0 mm stock from +0.4 mm stock in the finishingpasses. In some implementations, first directing can consist ofperforming two to five semi-finishing slices, and the second directingcan consist of performing two to four finishing slices.

While this specification contains many implementation details, theseshould not be construed as limitations on the scope of the invention orof what may be claimed, but rather as descriptions of features specificto particular embodiments of the invention. Certain features that aredescribed in this specification in the context of separate embodimentscan also be implemented in combination in a single embodiment.Conversely, various features that are described in the context of asingle embodiment can also be implemented in multiple embodimentsseparately or in any suitable sub-combination. Moreover, althoughfeatures may be described above as acting in certain combinations andeven initially claimed as such, one or more features from a claimedcombination can in some cases be excised from the combination, and theclaimed combination may be directed to a subcombination or variation ofa subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments.

Thus, particular embodiments of the invention have been described. Otherembodiments are within the scope of the following claims. In addition,the actions recited in the claims can be performed in a different orderand still achieve desirable results.

1-11. (canceled)
 12. A Computer Numerical Control (CNC) systemcomprising: two or more CNC machining tools; and a computer including aprocessor and a computer-readable medium, wherein the computer-readablemedium encodes instructions of a single Numerical Control (NC) programthat, when run on the processor causes the computer to control aselected one of the two or more CNC machining tools to performoperations comprising alternating between (i) moving the selected one ofthe two or more CNC machining tools along a semi-finishing toolpathsegment using a first set of spindle speed and feed rate values toremove a next portion of rough stock material in a next region of ablade or aerofoil being manufactured, and (ii) moving the selected oneof the two or more CNC machining tools along a finishing toolpathsegment to remove a semi-finishing thickness portion of the blade oraerofoil in the next region, wherein the first set of spindle speed andfeed rate values are different from the second set of spindle speed andfeed rate values, wherein each of the semi-finishing toolpath segmentand the finishing toolpath segment tracks fully around the blade oraerofoil, and wherein the CNC system is configured to receive a changeto a stepover/stepdown value used for the alternating semi-finishing andfinishing toolpath segments.
 13. The CNC system of claim 12, whereineach respective set of spindle speed and feed rate values specifyspindle speed and feed rate values for each point connecting segments ofa toolpath.
 14. The CNC system of claim 12, wherein the operationscomprise slowing feed rate and spindle speed of the selected one of thetwo or more CNC machining tools around leading and trailing edges of theblade or aerofoil.
 15. The CNC system of claim 14, wherein theoperations comprise gradually speeding up and slowing down spindle speedand feed rate of the selected one of the two or more CNC machining toolsacross a set distance when approaching or leaving one or more predefinedportions of the blade or aerofoil. 16-20. (canceled)
 21. The CNC systemof claim 12, wherein the CNC system is configured to gradually changespindle speed and feed rate over a given distance.
 22. The CNC system ofclaim 21, wherein each respective set of spindle speed and feed ratevalues specify different spindle speed and feed rate values for a firstpoint and a second point connecting segments of a toolpath, and whereinthe CNC system is configured to constantly vary spindle speed and feedrate between the first point and the second point, the constantlyvarying spindle speed and feed rate starting at the spindle speed andfeed rate specified for the first point and ending at the spindle speedand feed rate specified for the second point.
 23. The CNC system ofclaim 12, comprising a Computer Aided Manufacturing (CAM) systemconfigured to assign different commands to respective toolpath pointsdefining a given toolpath, including different spindle speed and feedrate values for the respective toolpath points, to facilitate finecontrol as the selected one of the two or more CNC machining tools movesalong the given toolpath.
 24. The CNC system of claim 12, wherein thesingle NC program, when run on the processor causes the computer toperform a combined semi-finishing and finishing operation, whichcomprises the alternating semi-finishing and finishing toolpathsegments, in a series of discrete levels from top to bottom of the bladeor aerofoil, and wherein spindle speed and feed rate values assignedrespectively to semi-finishing and finishing passes of the combinedsemi-finishing and finishing operation are tuned for each respectivelevel in the series of discrete levels from top to bottom of the bladeor aerofoil.
 25. The CNC system of claim 12, wherein the single NCprogram, when run on the processor causes the computer to control asecond selected one of the two or more CNC machining tools to perform aroughing operation on the blade or aerofoil before the alternatingsemi-finishing and finishing toolpath segments.
 26. The CNC system ofclaim 25, wherein the single NC program, when run on the processorcauses the computer to perform the roughing operation in a single passfrom top to bottom of the blade or aerofoil before performing a combinedsemi-finishing and finishing operation, which comprises the alternatingsemi-finishing and finishing toolpath segments, in a single pass fromtop to bottom of the blade or aerofoil.
 27. The CNC system of claim 25,wherein the single NC program, when run on the processor causes thecomputer to perform the roughing operation in a series of discretelevels from top to bottom of the blade or aerofoil and also perform acombined semi-finishing and finishing operation, which comprises thealternating semi-finishing and finishing toolpath segments, followingthe roughing operation in the same series of discrete levels.